How I learned to stop worrying and love graphene

Five years ago, I was staring out one of the few windowed cubicles in a cluttered office full of overambitious salespeople willing to throw their own father under a bus, if it meant a couple more dollars in commission and maybe a few more brownie points from the sweaty, beer-bellied sales manager. What was going through my mind as I stared out that window? Often nothing, sometimes an In-N-Out double-double with whole grilled onions, and every so often I would imagine I had a career with guts… substance. A career that I wouldn’t inaudibly mutter under my breath as an answer when asked the inevitable initial small talk question, “Well, what do you do?” A career that I would proudly proclaim to the world.

In front of the CAPSI House at Caltech, where we play with lasers in the name of enhancing high school education.

Early in life, there was always an attraction towards teaching, and during college I took education courses in route to becoming a high school teacher. However, money, that enticing savage, redirected my path away from education and into the world of sales, where feelings of shame (due to the high cheese-factor associated with the job) and satisfaction (due to the substantial pay check) took turns dominating my feelings regarding my career choice. Eventually, the cheese-factor won out and I needed a way out. So, I left the sales job and fell back on what I initially set out to do – teach.
Fast forward five years and I am now teaching physics at the high school level and contemplating my route to graduate school in physics. A recent highlight of my career as a high school physics teacher emerged as an opportunity for an internship at Caltech. I was given a choice to be involved in one of four different experiments and chose the lasers because lasers are cool. Well, apparently I am not the only one with those feelings for lasers, so I got bumped to graphene. I did not initially choose graphene, because my ignorance and fear of something new (wow, I might actually learn something) dictated my decision. Now, I could not be happier with my group and what I have learned in just a few weeks. And what a surprise… growing graphene is cool!

The following excerpt outlines the graphene experiment that I have been involved in here at Caltech with a question and answer format, more to keep me focused while writing than for your overall reading pleasure.

What is graphene?

One atom thick.

Graphene is a collection of carbon atoms attached together in a hexagonal lattice forming layers, or sheets, similar in structure to honeycomb and chicken wire. Amazingly, the thickness (or more appropriately, the lack thereof) of these layers, or sheets, is just one carbon atom. When graphene is stacked in multiple layers it forms graphite. Yes, the same graphite used in pencils. For a surprisingly interesting read on pencils and a little history on graphite, click here: http://www.pencils.com/unleaded-pencil.

So, why bother growing graphene at Caltech?

Since graphite consists of many layers of graphene stacked one on top of the other, then why not simply peel chunks of graphite like an onion and voila! This was the idea initially and the process of exfoliation, or cleaving, of Highly Oriented Pyrolytic Graphite (HOPG) using the Scotch tape method (pulling tape off chunks of graphite) yielded tiny fragmented flakes that served great for study, but contributed little towards manufacturing devices. Today, sheets of graphene are being sold, however, the price is high due to the substrate (silicon carbide) on which the graphene is grown. Now that demand for graphene has skyrocketed due to its desirable electrical properties (see this Nobel Prize), a race has begun to find a cheaper, more innovative technique for acquisition. Growing graphene on a metal substrate, such as nickel or copper, produces a very consistent, even monolayer of graphene that can be a much cheaper alternative to using the more expensive silicon carbide substrate.

OK, then what is the goal for graphene growth at Caltech?

Simple! Perfect a cost-effective technique for growing sheets of monolayer graphene and successfully transfer (without destroying) the graphene onto a silicon dioxide substrate, in a highly reproducible and consistent manner.

How can we tell if we have successfully grown this stuff?

Setting up for Raman Spectroscopy at the Yeh lab.

We are using Raman Spectroscopy to detect the presence of graphene on the metal substrate. If a thin layer of graphene is detected, Scanning Tunneling Microscopy (STM) is used to get a more detailed image of the landscape. STM is capable of non-destructive atomic resolution using quantum tunneling… very detailed. Adherence to ambiguity regarding the precise conditions of growth is intentional, since there have been no publications on the exact techniques we are using. Optimistically, if the techniques are a success, you will read about the findings in a not-so-distant future publication!

What’s so special about graphene?

Graphene has been shown to transport electrons extremely fast, which makes it a fantastic candidate for electronic devices. In fact, graphene can transport electrons tens of times faster than silicon, so naturally, transistors made of graphene have tremendous benefit over silicon due to their increased speed and dramatically reduced size (remember, graphene is one carbon atom thick.) It is well-known that silicon will not perform well when scaled down to very small sizes, so when compared to graphene it loses on two very important accounts – size and speed. There are some major problems with graphene (such as its inability to turn off current), which I would suggest researching if this is a personal area of interest.

Why should anyone care about transistors made of graphene?

One of the nearly countless possible applications for graphene is inside the microchip, maybe in conjunction with silicon. Graphene transistors are extremely small compared to their silicon counterpart, so the sheer number of graphene transistors able to be placed inside a microchip far exceeds the number for silicon transistors. This may serve as a remedy as far as perpetuating Moore’s Law and preventing the well-known 18 month doubling rate for the number of transistors on integrated circuits from screeching to a halt due to simply running out of bulky silicon transistor real estate. This, all in an effort to buy us some much-needed time until quantum computers are realized in every home and business.

Here’s my final thought: Relative to what I knew about graphene before my experience at Caltech, I have already learned quite a bit. Relative to what there is to know about graphene, I will have learned very little. However, that is inconsequential. What is consequential about this experience at Caltech is my deepening realization of the fact that science and its experiments are often dirty, dangerous, wrought with trial and error, extremely tedious, research heavy, occasionally awe-inspiring, and fascinatingly rewarding if you have a love for science and the vision that true joy mostly lies not in discovery, but in the journey. And that’s cool.

Please consider responding with much more interesting ideas than mine for graphene – it shouldn’t be difficult. I look forward to reading your replies!

Editor’s note: Benjamin Fackrell is a high-school physics teacher in the Pasadena Unified School District. He is part of IQIM’s Summer Research Institute, a six-week program designed to expose local physics teachers and high-school students to cutting-edge research taking place at Caltech’s research labs. He is currently working with the Yeh Group and is a member of IQIM’s Curriculum Development team, a group of teachers, students and Caltech postdocs, who are working to bring Quantum Mechanics to High Schools across the state through interactive simulations and hands-on experiments with lasers, polarizers and slit-films.

11 Comments

Nice question David! When the microscope’s (very thin) tip is brought really close to the surface we want to probe (just a few carbon atoms away), the conductivity of the tip’s material allows electrons from the surface to (quantum) tunnel through the vacuum to the microscope’s tip, creating a measurable current. The current depends on the voltage bias at the microscope’s tip (which can be fixed to some value), but it also depends on the position of the tip and the local density of states at that position (how many electrons are available for tunneling on the surface). I am not an expert, so I assume that the images we see produced by the microscope map darker areas to positions of the tip where the current is larger. For more details, look at the link for STM in the article above, or go to Wikipedia’s article on STM. Maybe one of the experts here can give a better answer?

Thanks for the encouraging words!
Yes, the internships are specifically directed to physics teachers from local high-schools. An even larger group of teachers (including the ones doing research) is involved with developing a 5-day physics module that explores quantum mechanics through lasers, prisms, polarizers and slit films. We have a great group, including recent high-school graduates, who are excited to bring this new hands-on experience into the classrooms!

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